1. Field of the Invention
The present invention relates to an implantable cardiac stimulating device of the type having a housing, a control circuit enclosed in the housing connected to a first electrode to be positioned to stimulate a first ventricle of the heart, the control circuit delivering stimulating pulses to the first electrode and varying the rate of stimulating pulses up to a maximum pacing rate, and the device having a sense amplifier for sensing at least one evoked response parameter from the first ventricle.
2. Description of the Prior Art
Cardiac stimulating devices of the above type are known in the art. The rate of stimulating pulses may be varied either in response to the sensing of an intrinsic atrial depolarization or by detecting the body's need for cardiac output by means of a sensor (a so-called sensor controlled/rate-responsive pacemaker).
Most pacers are arranged to stimulate the right ventricle of the heart, but it is also known to stimulate the left ventricle. In particular for the treatment of congestive heart failure or other severe cardiac failures it is known to stimulate the left ventricle, or both ventricles, in order to optimize the hemodynamic performance of the heart.
U.S. Pat. No. 5,728,40 describes a method and an apparatus for pacing the left ventricle of the heart. The pacing electrode is positioned within the interventricular septum proximate the left ventricular wall thereof.
U.S. Pat. No. 5,720,768 describes different possible electrical positions in order to stimulate or sense the different chambers of the heart.
Also the article “A Method for Permanent Transvenous Left Ventricular Pacing” by Blanc et al, PACE, Vol. 21, 1998, pp. 2021-2024, describes a method for positioning leads for left ventricular pacing.
U.S. Pat. No. 4,928,688 describes a method and an apparatus for treating patients suffering from congestive heart failure by stimulating both the ventricles. The document discusses the problem of the left and right ventricles contracting asynchronously. In order to effect substantially simultaneous contraction of both ventricles, the document suggests means for separately processing sensed cardiac signals from each of the right and left ventricles. If ventricular contractions are not sensed in both the ventricles within a period of coincidence defined by a time delay, the pacing pulse will be emitted at the end of this time delay, but only to the ventricle for which a QRS-complex has not been sensed. The time delay is suggested to be in the order of 5-10 ms.